1. Field of the Invention
This invention relates to dynamoelectric machines having commutators and brushes, and more particularly to direct current electric motors and generators and to features of the design of brushes used in such machines.
2. Description of the Prior Art
Conventional machines use cored-type brushes in which the cores extend perpendicular to the cross-sectional plane which is perpendicular to the sides of the brush. These brushes thus extend in a plane that is essentially parallel to the direction in which the brushes move toward the commutator as the brushes wear.
As the brush rides on the surface of the commutator, a film develops on the outer surface of the commutator. This film has an abrasivehess depending upon the brush material, the core material, the commutator material and ambient conditions. Under certain conditions the film that develops under the cores in the brush is more abrasive to the commutator surface than the film that develops under the remaining part of the brush. This difference in abrasiveness can cause non-uniform wearing of the commutator surface. This uneven wearing of the commutator can affect the maintenance and performance of the motor. When the commutator wears unevenly, it is often necessary to resurface the commutator when the brushes are replaced in order to achieve effective contact between the brushes and the commutator and to maintain proper operation of the motor.